(1) Field of the Invention
This invention relates to a nonreversible freeze-thaw indicator which will detect whether an article has been subjected to freezing or thawing conditions, with particular reference to an encapsulated translucent to opaque colloidal dispersion of organic solid particles in a liquid medium which becomes nonreversibly destabilized upon freezing and which thereafter provides a telltale visual sign if the dispersion rises through its freeze-thaw temperature.
(2) Description of the Prior Art
Many products, when subjected to freezing or thawing conditions, deteriorate rapidly to the point where they are seriously affected by loss of quality or are rendered totally unusable. For example, foods such as mayonnaise, fabric softeners, latex products such as paints, concrete modifiers, laboratory supplies, biological samples such as whole blood and the like can be seriously affected or lost when subjected to freezing conditions. In addition, products which need to be kept well frozen such as meats, vegetables, ice cream and the like can lose flavor and texture or even spoil if they are not maintained in a frozen condition. Often, the adverse effects of freezing or thawing conditions on such products cannot be later detected by the appearance of the products. Therefore, it is important to both the seller and buyer of such products that some indicator means be provided which will signal a change in products caused by freezing or thawing conditions.
In the past, many temperature indicators have been proposed, but none to our knowledge have been found to be completely satisfactory or commercially acceptable. Generally the prior art detectors have been characterized by their cumbersome size or intricate construction and have tended to be unreliable and inaccurate. In addition, they generally have poor stability and shelf life at normal storage temperatures.
One known prior art thermosensitive indicator is illustrated by U.S. Pat. No. 2,971,852. This indicator utilizes an emulsion of oil in water, water in oil or oil in oil to record if a temperature rise above its freezing point has occurred since the emulsion will break and separate into two phases after it has thawed. The emulsion indicator differs from the present invention not only in that it utilizes an emulsion rather than the colloidal dispersion or organic solid particles in a liquid media, but also in that it can only be reliably used as a thaw indicator since emulsions are generally unstable in the liquid state at normal storage temperatures and will quickly separate into two phases. Therefore, the emulsion indicator has only a short shelf life above freezing temperatures after being made and must be quickly transformed to its frozen state and used as a thaw indicator to be accurate and reliable.
Accordingly, it is an object of the present invention to provide an improved nonreversible freeze-thaw indicator adapted to detect whether an article has been subjected to freezing or thawing conditions. Another object of the present invention is to provide an indicator that can be easily and economically produced and stored for an indefinite period of time at normal or elevated temperatures without loss of effectiveness. A further object of the present invention is to provide an indicator which can be easily utilized and is reliable and accurate. Other objects of the present invention will be apparent from the following specification, drawings and claims.